To apply a light emitting device for lighting, a white light has to be gained by using an LED. There may be three well known methods to realize a white semiconductor light emitting device.
The first method realizes a white light by combining three light emitting diodes (LED) which emit three primary colors of red, green and blue colors. The second method realizes the white light by excitation of three primary color phosphors, using an ultraviolet LED as lighting source, and it uses R, G, and B phosphors as light emitting materials. The third method realizes the white light by excitation of a yellow phosphor, using a blue LED as lighting source and it generally uses YAG:Ce phosphor as light emitting material.